Heat pumps have long been known and employed in the heating, ventilating, and air conditioning industry. A significant reason for the extensive use and focus of attention on heat pump systems is that the same components may be employed to effect both heating and cooling operations, whereas most other systems require a substantial number of separate equipment components for carrying out heating and cooling functions. Classically, heat pump systems employ a compressor which is operated by an electric motor to circulate refrigerant through a condenser which converts a gaseous form of the refrigerant to a liquid and an evaporator which absorbs heat from or imparts heat to an area to be cooled or heated, respectively, while converting the refrigerant from a liquid to a gaseous form.
For the most part, advancements in heat pump system technology have been directed to the development of improved working fluids and system components. In the case of working fluids, different refrigerants and particularly different fluorocarbon compounds have been developed which exhibit optimum performance characteristics in particular equipment or operating ranges. In regard to system components, efforts have been made to improve the operation and efficiency of the compressor, condenser, evaporator, and any ancillary components of these systems. However, due to the relatively advanced age and state of development of this technology, only minor improvements in operation and efficiency have been achieved through research and development efforts of this nature over the years.
In recent years, attempts have been made to develop heat pumps which are heat driven. In this respect, engine driven and absorption type heat pumps represent examples of efforts of this type. Heat driven heat pumps of these types have not achieved commercial acceptance and recognition for a number of reasons. In general, devices of this nature tend to be highly complex systems having component elements which are both sophisticated and expensive. In addition, many of these systems contemplate the use of working fluids which are other than conventional refrigerants, such as ammonia or lithium bromide. Due to the fact that ammonia, for example, is considered to be a noxious gas, the use of nonconventional working fluids of this nature requires radically new and different capabilities and equipment with respect to installation, repair, and service personnel than is normally involved in the heating, ventilating, and air conditioning industry. With the technical limitations on working fluid and component improvements and the lack of commercial acceptance of heat driven heat pump systems, heat pump systems have remained in essentially the same technological state of development for a substantial number of years.